1. Technical Field
This invention is related to a communication system and a communication method, and particularly to control of transmitting power.
2. Background Art
FIG. 1 shows a partial construction in a communication system of CDMA (Code Division Multiple Access), in which reference numeral 1 is a PSTN (Public Switched Telephone Network), 2 is an RNC (Radio Network control apparatus), 3 is a plurality of BTS's (Basic Station), 4 is a mobile terminal which performs radio communication between the BTS 3, and 5 is a cell which is a range allowing communication between each BTS 3.
Now, the operation is described.
When the user of any mobile terminal 4 in a cell 5, which is capable of radio communication by down-link transmitting power, inputs a telephone number to originate a call (access), the BTS 3 corresponding to the cell 5 responds to the call and receives the radio signal from the mobile terminal 4. And, it identifies the mobile terminal 4 from the demodulated signal obtained by demodulating the received radio signal, and identifies the called terminal from the telephone number contained in the demodulated signal. Then, the connection request information for them is transmitted to the RNC 2.
RNC 2 responds to the connection request information to perform the connection control between the originating mobile terminal 4 and the called terminal. That is, if the called terminal is in another network, that information is sent to the PSTN 1. Or, if the called terminal is a mobile terminal 4 in the same radio network, the connection request information is sent to all the accommodated BTS's 4. Each BTS 4 originates a call to the mobile terminal 4 existing in the corresponding cell 5 to call the telephone number.
If the mobile terminal 4 corresponding to this telephone number exists in the cell allowing radio communication by the transmitting power of any BTS 3, it responds to the call to notify the user of an incoming call. And, if the user responds to the incoming call, a communication channel is established between the mobile terminal 4, which is the calling terminal, and the mobile terminal 4 which is the called terminal, and voice data is transmitted and received. If one or both in communication move from the region of the current cell into the region of another cell, the BTS 3 corresponding to the current cell senses that, and notifies the RNC 2 of the movement of the mobile terminal 4. The RNC 2 performs so-called handoff processing in response to the notification.
Further, the RNC 2 defines the maximum reference value and the minimum reference value of the mobile terminal 4 that can access each accommodated BTS 3, and sends common pilot transmitting power to control the transmitting power to the mobile terminal. As a result, as shown in FIG. 2, the BTS 4 adjusts the radius (field strength of transmitting power) of the corresponding cell 5. For instance, if the radius of the cell is assumed to be R1 when the number of mobile terminals 4 (referred to as “traffic number” is in a prescribed range, the radius of the cell 5 is set to R2 to expand the range allowing communication if the number of mobile terminals 4 decrease below the minimum reference value. Conversely, if the number of mobile terminals 4 exceeds the maximum reference value, the radius of the cell is set to R3 to narrow the range allowing communication.
FIG. 3 is a flowchart showing the operation of the cell radius adjustment, and in the figure, it is determined whether or not the traffic number has exceeded the maximum reference value (step ST1), and the cell radius is reduced if exceeded (step ST2). Further, it is determined whether or not the traffic number had decreased below the minimum reference value (step ST3), and the cell radius is extended if decreased (step ST4).
However, in the above conventional communication system and communication method, since the radius is reduced or extended for a certain cell alone, there is a problem that interference or traffic maldistribution in a plurality of cells occurs. Further, since the mobile terminals 4 do not always concentrically exist around the BTS 3, there is a problem that traffic control is insufficient with the conventional power control by adjustment of the cell radius.
The present invention was accomplished to solve the above described problems, and it aims to reduce interference and eliminate traffic maldistribution in a plurality of cells. Further, it aims to enable sufficient traffic control in a cell or in a plurality of cells.